In a house only 3 years old I have 2 large ((41 X 58 in) brick chimneys. They are just wood framed and bricked since the fireplaces are direct vented to the outside. They have a thin layer of concrete on top which is leaking into the house. I had a roofer apply some type of polymer coating last year. It dried hard and seemed to work for a few months but has since cracked and is chipping off and they are leaking again. The concrete top is not sloped and holds the water on top until it starts seeping down the inside of the chimney. What type of repair company should I be looking for and how will know if they are repairing it correctly? Thanks for any help or hints you can provide.

Sounds like you need a certified, chimney installer. The better ones are available from a wood/pellet stove company that sells the stoves and the pipe. These folks are certified in the products they install from the manufacturers, and they do this for a living.
Ask around for a good company, someone you know has a stove I'm sure. Welcome aboard.